Many vaccine candidates induce a strong, but transient antibody response, which makes the vaccine impractical for protection over years when the timing of exposure to the relevant agent cannot be predicted (i.e., other than with travelers going to an endemic area or troops arriving on station). Therefore, the primary goal of this project is to identify those aspects of adaptive T-cell dependent antibody responses that control the persistence of high antibody levels after vaccination, with a specific focus on the choice of adjuvant in the vaccine formation. Using a combination of rodent and NHP studies, we seek to identify whether and to what extent the quantity and quality of T cell help (Tfh) for B cell responses, the specific conditions involved in B cell activation by antigen, and the state and regulation of the bone marrow plasma cell niche individually and in aggregate contribute to robust, long-lived antibody responses. These studies will employ both candidate malarial vaccine antigens in combination with a wide range of adjuvants. Adjuvants that may not be directly useful in humans will be included in the analysis, because discovery of the mechanisms(s) by which they foster the desired responses can provide guidance in development of acceptable alternatives for human use. Insight from these animal studies will be used to guide immunological studies and vaccine design for early stage human vaccine trials using malarial antigens. In FY18: We highlight here our published results: TLR-adjuvanted nanoparticle vaccines differentially influence the quality and longevity of responses to malaria antigen Pfs25. With collaborators at Karolinska and elsewhere, we contributed to nonhuman primates that demonstrate that multiple aspects of Pfs25 immunity were enhanced by antigen encapsulation in poly(lactic-co-glycolic acid)-based (PLGA)-based synthetic vaccine particles (SVPPfs25) and potent TLR-based adjuvants. While Pfs25-specific B cells were responsible for increasing Ab titers, T cell responses stimulated increased Ab avidity. The innate immune activation differentially stimulated by the adjuvants revealed a strong correlation between type I IFN polarization, induced by R848 and CpG, and increased Ab half-life and longevity. Collectively, the data identify ways to improve vaccine-induced immunity to poorly immunogenic proteins, both by the choice of antigen and adjuvant formulation, and highlight underlying immunological mechanisms. Safety and immunogenicity of Pfs25H-EPA/Alhydrogel, a transmission-blocking vaccine against Plasmodium falciparum: a randomised, double-blind, comparator-controlled, dose-escalation study in healthy Malian adults. In this double-blind, randomized, comparator-controlled, dose-escalation trial in Bancoumana, Mali,, we assessed Pfs25H-EPA/Alhydrogel for safety and functional immunogenicity in Malian adults. Pfs25H-EPA/Alhydrogel was well tolerated and induced significant serum activity by standard membrane feeding assays but transmission blocking activity was not confirmed by weekly direct skin feed. This activity required four doses, and titres decreased rapidly after the fourth dose. The results emphasize the need for new platforms, such as newer adjuvants that can induce more durable antibody responses. In unpublished work, we established a Research Collaboration Agreement with the Walter Reed Army Institute of Research (WRAIR) to obtain potent adjuvants with clinical potential. We are using these Army Liposome Formulation (ALF)-based adjuvants, in combination with carrier-specific tetramers to relate Tfh quality and quantity to vaccine outcome. We are now testing different antigen/adjuvant ratios in mice to determine whether fractional dose of one or both components are important. In addition, we are performing experiments to characterize a critical responding/target cell of 3rd dose by examining a role of memory T follicular helper lymphocytes vs. activation of memory B cells in a T cell independent manner. In an ongoing experiment, we have initially established that a fractional boosting dose in mice induces antibody titer that is similar to that induced from a full dose, thereby recapitulating human observations with the RTS,S vaccine. Additionally, this boost is dependent on CD4+ T cells, as in vivo depletion eliminates the boost response.